1. Field of the Invention
The present invention relates to an optical waveguide device which is preferably applicable to a light modulator in an optical fiber gyroscope or the like. The present invention also relates to an assembly including such an optical waveguide device and an optical fiber holding substrate.
2. Description of the Related Art
In the fields of optical measurement systems, optical communication systems, etc., it is known to manufacture optical waveguide devices by forming three-dimensional optical waveguides on substrates made of various electro-optic monocrystals, glasses or resins. As for such optical waveguide devices, there have been known optical branch devices, optical modulation devices, optical deflection devices, optical switches, multiplexers, etc. These waveguide-type devices have attracted considerable attention because of advantages such as smallness in size, good stability, reduced driving power and high speed signal transmission.
The present inventor has investigated manufacture of optical waveguide devices through the formation of what is called a three-dimensional optical waveguide of Y-branch type on a substrate made of LiNbO.sub.3, and uses of such devices as modulators for fiber optic gyroscopes. The modulator for fiber optic gyroscopes is an instrument for measuring Sagnac effect which is generated when an optical fiber coil is rotated, and is known to have following applications.
(1) Navigation systems for vehicles such as automobiles, aircraft, shipping, etc.
(2) Tilt sensors and rotation sensors for measuring changes in the posture of a vehicle. As the changes in a vehicle posture, mention may be made of a tilt of an automobile caused by sinkage of a suspension, a rolling of an aircraft and the like.
In FIG. 1, there is schematically shown an example of such fiber optic gyroscopes. Light emitted by a light source 1 is transmitted through an optical fiber 3. The light passes through a fiber coupler 4, propagates as shown by an arrow A and impinges on an optical waveguide substrate 5. The light impinging on the optical waveguide substrate 5 is divided at a Y-shaped dividing point into two branch-waveguides, emanates from the optical waveguide substrate 5, and then impinges on a fiber coil 6. The light emanating from one of the branch-waveguides propagates as shown by an arrow B and is made incident upon the fiber coil 6, while the light emanating from the other branch-waveguide propagates as shown by an arrow C. Both of the light passed through the fiber coil 6 are made incident again on respective branch portions, reversely propagate the above-explained optical paths to the fiber coupler 4 and then impinge on a detector 2. Incidentally, in the optical waveguide substrate 5, a polarizer, a beam splitter and a phase modulator are integrated on a chip-shaped optical waveguide substrate. Due to this constitution, the total production cost of a fiber optic gyroscope can be reduced, while improving the performance thereof.
FIG. 2 is a plan view illustrating a construction of an example of such optical waveguide device.
A branch-type optical waveguide, what is called a Y-shaped optical waveguide 10 is formed between end faces 8a and 8b of a substrate 8 of the optical waveguide device 5. The optical waveguide 10 is constituted by a stem portion 10a, a dividing point 10b and branch portions 10c, said stem portion, dividing point and branch portions being continuously ranged in this order when viewed from the end face 8a side, and said branch portions 10c extending up to the end face 8b. A polarizer 9 is arranged on the stem portion 10a and controlling electrodes 11 and 12 are formed along each of the branch portions 10c so as to sandwich the branch portion with the electrodes.
In order to align and couple an end face of an optical fiber 3A on the entrance side with that of the stem portion 10a, the terminal portion of the optical fiber 3A is fixedly held by an optical fiber holding substrate 7A and an end face of the holding substrate 7A is adhered onto the end face 8a of the optical waveguide device 5. Similarly, in order to align and couple end faces of optical fibers 3B and 3C on the exit side with those of the branch portions 10c, the end portions of the optical fibers 3B and 3C are fixedly held by an optical fiber holding substrate 7B and an end face of the holding substrate 7B is adhered onto the end face 8b of the optical waveguide device 5.
Although it would be varied depending upon the operation method used, the fiber optic gyroscope is most generally operated in the following manner. Light is incident on the stem portion 10a of the optical waveguide 10 and divided at the dividing point 10b at a ratio of 50:50(%). Then, divided light along one of the branches 10c is phase-modulated by applying a predetermined voltage to the electrodes. A phase difference due to the Sagnac effects, which is generated by the rotation of the optical system 6, is detected by the optical waveguide device. The thus-obtained phase difference is introduced into a formula showing the relation between a rotational angular velocity of the optical system and a phase difference to attain a revolution speed.